1. Technical Field
The present invention relates generally to cylinder liners for diesel engine applications and to methods of their manufacture.
2. Related Art
It is anticipated that government regulations will soon require the recirculation of exhaust gases in diesel engines, which would present a much more corrosive, acidic operating environment for engine liners than that presently experienced in diesel engines. Many current ferrous cylinder lines would be prone to corrosive attack under EGR conditions. While it is not uncommon to coat cylinder liners with a metallic wear surface, such coatings are typically post-plate honed or finished to achieve the desired, final surface finish. However, such honing or finishing of the coating surface would likely disturb the coating, impairing its effectiveness as a barrier in a diesel EGR environment.
It is an object of the present invention to provide a cylinder liner and method of its manufacture which is resistant to corrosion in diesel engine EGR operating conditions.
A method according to the invention of manufacturing a cylinder liner for a diesel engine having an exhaust gas recirculation system (EGR) comprises fabricating a cylinder liner of ferrous metal having an inner surface and finishing the inner surface to the desired final surface finish for guiding the piston. After final finishing, a continuous, non-porous EGR barrier coating of chromium is applied to the finished inner surface, and the liner is operated in an EGR environment of a diesel engine without any post-bonding machining of the metallic EGR coating.
The invention has the advantage of providing a barrier coating to an otherwise conventional ferrous liner that enables the liner to operate in a corrosive EGR environment of a diesel engine without being adversely affected by the environment.
The invention has the further advantage of providing a simple solution to the problem of how to protect a ferrous liner in an EGR diesel engine environment. In particular, the invention provides a post-machined coating to the otherwise final-finished liner. The coating is continuous and non-porous and is presented in its as-coated condition to the EGR environment. Eliminating any postcoating machining of the EGR coating ensures that the coating remains continuous and non-porous and is not disturbed so as to impair its barrier properties to the EGR environment.
Another advantage offered by the invention is its simplicity in addressing the problem. The invention recognizes that careful attention to the process steps, the selection of the coating material and the preservation of the coating once applied, provides a simple but effective barrier for protecting a ferrous liner from the EGR environment of a diesel engine.
The invention further simplifies the process of manufacturing cylinder liners by eliminating any post-coating finishing operations on the coating. Once coated, the liner is ready to be installed in a diesel engine. The final finish of the inner surface of the liner and careful attention to the application of the coating provides the coated liner with the desired running surface without having to disturb the coating after it is applied.